Heat exchanger apparatus

ABSTRACT

Heat exchanger apparatus in which heat is transferred between two moving fluids, one of said fluids being the heating fluid and the other of said fluids being the fluid to be heated, which comprises a first flow path for said heating fluid, a second flow path for said fluid to be heated, a rotatable cylinder separating said first flow path from said second flow path, and fan or pump means operatively associated with said first and said second flow paths to promote movement of said heating fluid relative to one surface of said rotatable cylinder and to promote movement of said fluid to be heated relative to the other surface of said rotatable cylinder.

United States Patent [191 Sugg [54] HEAT EXCHANGER APPARATUS [75] Inventor: Philip Crawford Sugg, Redhill, En-

' gland [73] Assignee: Thorn Heating Limited, Crawley,

Sussex, England [22] Filed: Jan. 25, 1971 21 App]. No.: 109,437

[30] Foreign Application Priority Data May 28, 1970 Great Britain ..25,730/70 [52] US. Cl ..263/20, 165/89 [51] Int. Cl ..F23l 15/04 [58] Field of Search ..263/20; 165/86, 89, 90

[56] References Cited UNITED STATES PATENTS 1,676,787 7/1928 Lissauer ..l65/90 6/l92l Snyder ..263/20 7/l969 Durand 165190 Primary Examiner-John J. Camby Attorney-Baldwin, Wight & Brown [5 7 ABSTRACT Heat exchanger apparatus in which heat is transferred between two moving fluids, one of said fluids being the heating fluid and the other of said fluids being the fluid to be heated, which comprises a first flow path for said heating fluid, a second flow path for said fluid to be heated, a rotatable cylinder separating said first flow path from said second flow path, and fan or pump means operatively associated with said first and said second flow paths to promote movement of said heating fluid relative to one surface of said rotatable cylinder and to promote movement of said fluid to be heated relative to the other surface of said rotatable cylinder.

PATENTEDJAN 16 I973 3, 71 l 074 SHEET 1 0F 3 HEAT EXCHANGER APPARATUS This invention relates to heat exhanger apparatus for transferring heat between two moving fluids and is more particularly concerned with such apparatus for transferring heat from a flame source to a gas such as air, although it will be obvious that is could also be applied to the heating of a liquid, or a combination of a gas and a liquid.

it is known that, for most flow passages that might be used for the transfer surfaces of heat exchangers, the transfer of heat per unit of area varies as a power, usually less than one, of the velocity of the fluid flow over the surfaces.

It is an object of the present invention to reduce the physical size of heat exchanger equipment. This object is achieved by providing apparatus in which the fluid velocities on one or both sides of the transfer surface is or are increased in such manner that the increase in power necessary to overcome the friction losses associated with such increased velocity is kept to a minimum.

According to the present invention, there is provided heat exchanger apparatus in which heat is transferred between two moving fluids, one being the heating fluid and the other being the fluid to be heated, characterized in that said fluids are separated by the wall of a rotatable chamber, and fan or pump means are provided in operative association with the rotatable chamber to promote movement of the heating fluid relative to one surface of the rotatable chamber and to promote movement of the fluid to be heated relative to the other surface of the rotatable chamber.

More particularly, the invention comprises heat exchanger apparatus in which heat is transferred between two moving fluids, one being the heating fluid and the other being the fluid to be heated, wherein said fluids are separated by the wall of a rotatable combustion chamber within which is housed stationary heating means which provide the heating fluid, and fan or pump means are provided in operative association with the rotatable combustion chamber to cause movement of the heating fluid over the internal surface of the combustion chamber and to cause movement of the fluid to be heated over the external surface of the combustion chamber.

According to the invention furthermore, there is provided heat exchanger apparatus for transferring heat between two fluids in which a heat transfer surface thereof, or at least a part of the total of said heat transfer surface, is provided by the blade elements of a fan or pump which is arranged to cause movement of the fluids through the apparatus.

According to the invention still further, the apparatus includes means for supplying, at a selected position or positions, a separate supply of one of the fluids at a pressure higher than that of the heating fluid and the fluid to be heated, in order to prevent without the necessity of using mechanical glands, mixing of the two fluids.

According to another aspect of the invention, the apparatus may be arranged and constructed so that, in use, it may be positioned in an outside wall of a building, the arrangement being such that at least the combustion air inlet and the exhaust gas outlet are positioned externally of said outside wall.

In a typical arrangement of the invention for gas/air heat exchange, the source of heat, preferably a gas flame, is provided to enter in an axial direction from a stationary burner into a rotating combustion chamber formed integral with the blades of a centrifugal fan provided to move the air over the outer surface of the heated combustion chamber to cause heat transfer to take place between the chamber and the air. These blades receive heat by conduction and by radiation, and transfer additional heat to the air moved by the fan. The rotating combustion chamber is also provided with a further centrifugal fan of suitable characteristics for the purpose of moving the products of combustion at an optimum velocity over the heat exchanger surface provided by the combustion chamber wall in order to heat said wall and to dispose of the products of combustion through an exhaust outlet. It is also preferred, in order to avoid the need for any mechanical glands between the stationary and rotating components, and to prevent escape of, or mixing of, the products of combustion with the main flow of heated air, to interpose between these two flows, in a position where a gland might otherwise be required, a small flow of sealing air at a pressure exceeding that of the two fluids. This is preferably effected in an area of small mechanical clearance to minimize the volume of sealing" air required and leakage of this air through the clearances into the products of combustion and main flow of heated air. The supply of sealing air could be derived from a centrifugal fan having characteristics to provide a pressure higher than that of the other fans on the rotating combustion chamber. it will be obvious that, as an alternative, mechanical seals could be used.

It will be appreciated that the components described above can be arranged in several different ways. However, two embodiments showing the relative positions of the components are illustrated by way of example in the accompanying drawings in which:

FIG. 1 is a longitudinal section through one embodiment of the apparatus, it being understood that, for convenience, the various inlets and outlets are shown in the same plane;

FIG. 2 is an end elevation corresponding to FIG. 1, and

F IG. 3 is a longitudinal section through an alternative embodiment of the invention.

Referring to FIGS. 1 and 2 of the drawings, the heat exchanger apparatus comprises a combustion chamber in the form of a cylinder 1 which is closed at one end by an end closure casting 2 which is coupled to the drive shaft 3 of an electric motor 4. The cylinder 1 is mounted in suitable bearings (not shown) and, in use, is rotated about its longitudinal axis by the motor 4.

Mounted within the cylinder 1 adjacent the end closure 2 is a stationary annular gas burner head 5 having a plurality of circumferentially disposed burner orifices 6. Gas to the burner head 5 is supplied by a gas pipe 7 which is disposed on the central longitudinal axis of the cylinder 1 and which is attached to a coupling spigot 8 which is adapted to be connected to a source of gas supply.

Primary air for combustion purposes is admitted to the gas pipe 7 via a spigot 9.

Arranged concentric with, and in spaced relationship with, the gas/air pipe 7 is a cooling or secondary air tube which is connected at one end to a spigot 11 so that cooling air can be circulated in the annular space between the gas/air pipe 7 and the tube 10 to cool the gas/air pipe 7. A plurality of holes 100 may be formed in the tube 10 to provide a secondary air flow into the combustion chamber.

A plurality of radially disposed vanes 12, for example four, are fixed to the cooling air tube 10 to extend lengthwise of the cylinder 1.

Mounted on the open end of the cylinder 1 is an annular bracket 13 which supports a plurality of radially disposed blades 14 providing a fan or pump. The fan or pump is arranged in a volute chamber 15 and serves, in use, to draw the products of combustion over the interior surface of the cylinder 1 and to expel them from the apparatus, via the volute 15, to atmosphere through a suitable flue.

Arranged adjacent the volute chamber 15 is a dilution air chamber '16 which communicates, through openings 17, with the combustion chamber. Dilution air is admitted to the chamber 16 via a spigot 18 having a variable inlet which is such as to provide controlled dilution of the combustion products so as to reduce condensation in the flue passages as is well known.

The chamber 16 is also formed with observation windows 19, which are coincident with the openings 17, to enable observation of the gas jets to take place.

Surrounding the rotatable combustion chamber 1 is a casing 20 which is spaced from the chamber 1 to present an annular passage 21 through which air to be heated is drawn. The casing 20 is formed at one end adjacent the volute chamber 15 with an air inlet 22 preferably in the form of a volute chamber, and at its other end adjacent the burner 5 with an air outlet 23, which is also preferably in the form of a volute chamber and is adapted to be coupled to a warm air ducted heating system. Such a system may be used, according to the size and capacity of the apparatus, to serve one or more rooms or areas.

Supported on the rotatable cylinder 1 within the air outlet 23 is a second set of radially disposed blades 24 providing a fan or pump which, in use, is arranged todraw air through the inlet 22 and to expel it through the outlet 23.

In operation,the cylinder 1 is rotated by the motor 4 and the gas jets are ignited, the products of combustion providing the heating fluid which is drawn over the interior surface of the cylinder 1 by the fan or pump 14 and expelled to atmosphere. Thus, the walls of the cylinder 1 provide a heat exchange surface which is heated by the heating fluid. In this respect, it will be appreciated that the provision of the stationary blades 12 will reduce the tendency of the heating fluid to be subjected to a swirling action, i.e. a tendency to co-rotate with the cylinder 1, and therefore increase the scrubbing action between the heating fluid and the interior wall of the cylinder 1 thereby increasing heat transfer. Stationary vanes can similarly be arranged externally of the cylinder 1, i.e. fixed to the casing 20, for the same purpose in respect of the fluid to be heated.

At the same time, air to be heated is drawn into the casing 20 by the fan 24, the arrangement of the inlet and outlets 22 and 23 being such that the air being moved over the external surface of the cylinder 1 has imparted thereto axial and circumferential components of movement which add to the scrubbing action of the air thereby enhancing heat transfer between the air being heated and the heat transfer surface of the cylinder 1.

It will be appreciated that the position of the fan 24 is such that the blades receive heat by conduction and by radiation from the combustion chamber 1 'and therefore the air will be further heated during its passage through the fan.

As previously described, a small flow of higher pressure sealing air is used to control the direction of leakage between the rotating and stationary components of the apparatus. Neither the fan nor the means for directing the sealing air are shown in the drawing but it will be understood that the air supply will be required at the position between annular bracket 13 and the volute chamber 15, the object being to prevent the products of combustion mixing with the circulating air and to prevent them leaving the apparatus other than by way of the flue.

In order to improve the efficiency of the apparatus, refractory elements (not shown) may be arranged in the four quadrants formed by the blades 12 so that the flames nearest the axis of the cylinder 1 enter into contact with and heat the refractory material. Thus, these elements will, in use, provide radiant heat to improve heat transfer to the cylinder 1. Alternatively, the blades 12 could be made of a refractory material, and also be inter-connected by webs of the same material.

It will be appreciated that, in the embodiment just described, the various inlets and outlets will, where necessary, be coupled to ducting. This is of course necessary particularly with the chamber 15 through which the products of combustion must be discharged to atmosphere. In order to avoid the use of ducting in this respect, the apparatus can be modified as shown in FIG. 3 and mounted in an outside wall of a building which wall is indicated at W.

The apparatus of FIG. 3 comprises a stationary tube 25 which serves to convey a gas/air mixture to a burner 26, the gas entering the tube 25 via a gas supply pipe 27 connected to a nozzle 28 and the air entering the tube axially from one end via a hooded inlet member 29. As can be seen from the drawing, the tube 25 extends beyond the external face of the wall W and the gas and air inlets are positioned so that mixing thereof takes place outside the premises to be heated.

A rotatable heat exchanger drum 30 is mounted concentrically about the tube 25 to present an annular passage for the exhaust gases from the burner 26. The drum 30 is mounted at its ends in bearings 31 and 32 and is rotated, via a driven pulley 33, by an electric motor (not shown), the arrangement ensuring correct alignment of the bearings and also permitting axial expansion of the drum 25. As can be seen from the drawing, the bearing 31 is positioned between the stationary tube 25 and the rotatable drum 30, and the bearing 32 is positioned between a stub axle 34 and a tube 35 flxed to the drum 30 on which tube 35 the pulley 33 is secured.

Mounted on the outer end of the drum 30 so as to be positioned externally of the wall W is a series of blades 36 providing a fan or pump which serves to circulate the gas/air mixture throughthe tube 25 and also to expel the products of combustion at a suitable velocity through the tube 30 and through a volute 37 to atmosphere.

At the inner or opposite end of the drum 30 is a second series of blades or vanes 38 providing a fan or pump which operates within a volute 39 and serves to draw circulating air over the drum 30 and to expel it either directly or indirectly into the area or areas to be heated. For this purpose an outer casing 40 and an inner dividing wall 41 are provided to present an inlet annulus 43 which communicates with the area to be heated and an air heating annulus 42 through which air is drawn through the annulus 43 and expelled through the volute 39. In this respect, and end guide element shown at 44, is arranged in spaced relationship with the outer end of the dividing wall 41 so as to guide the air from the annulus 43 into the annulus 42. Furthermore, the element 44 is positioned in line with the face of the wall W and is spaced from the volute 37 to present a head break zone 45 separating the air to be heated from the products of combustion.

In the latter respect, the action of the fan 36 produces a negative pressure at point 46 where there is a small mechanical clearance between the volute 37 and the rotating drum 30. Similarly, the action of the circulating air fan 36 produces a negative pressure at point 47 where there is a small mechanical clearance between the element 44 and the rotating drum 30. Thus, it will be appreciated that air freely entering the head break is drawn in at both points 46 and 47 thereby ensuring complete separation of the circulating air and the products of combustion without the need for a mechanical seal.

In the latter respect, it will be appreciated that, because the pressure of the products of combustion and the circulating air is sub-atmospheric, an adequate supply of air at atmospheric pressure up to a definable limit of air intake/flue outlet system resistance related to the power and design of the flue fan, will provide the necessary seal. ln the case of the embodiment of FIGS. 1 and 2 this resistance, referred to as the combustion system resistance, will vary with the length, diameter etc. of the exhaust and inlet pipes used to connect the apparatus to a terminal outside the building. In the case of the present apparatus, the combustion system resistance is fixed by integral parts of the apparatus and separation of the flows is achieved without relaying on the correct choice by the installer of the pipe system and other factors.

That portion of the apparatus which is outside the wall of the building will be protected against the ingress of rain by means ofa suitable hood and will be guarded, in accordance with standard practice, to prevent the entry of birds etc.

It will be appreciated that any transient changes in the local air pressure due to wind effects will be substantially equal on the closely grouped inlet and exhaust openings and can therefore be balanced by suitable design.

lt will further be appreciated that, as compared with the embodiment of FIGS. 1 and 2 which requires pipes to convey air and gases to and from theexterior of a building, because the only duty of the fan 36 is to circulate the gas/air mixture to the burner, and to expel the products of combustion from the burner, the fan 36 can be of relatively small diameter. In this respect, it is preferable'that the fan 36 should be of the same, or smaller, diameter as that of the 'outer casing 40 to facilitate the mounting of the apparatus in an opening in the wall W.

It will be understood that other features used in air heating systems, such as filtration etc., can be readily included in, or in association with, the presentapparatus. Furthermore, the apparatus of the alternative embodiment may also include other means such as the fixed vanes and refractory elements for improving the efficiency thereof, as described with reference to the embodiment of FIGS. 1 and 2.

The invention may be used for heating one or more rooms or areas for either domestic, commercial or industrial premises. For industrial premises it may be found advantageous to mount the apparatus to extend through a roof.

Although the invention has been described with reference to heating, it is envisaged that, during the summer months, the embodiment of FIG. 3 can be used for forced ventilation. In this respect, means will be provided to move the element 44 axially into the space 45 whereby the fan 38 will induce some outside air to be expelled into the room or area. Furthermore, by providing means to close the annulus 43, it will be appreciated that only outside air will be expelled into the room or area.

lt will be understood that the apparatus according to the present invention attains high scrubbing action both internally and externally of the rotating combustion chamber thereby providing maximum heat transfer. Furthermore, it has the advantage that, by.virtue of the fact that the combustion chamber is rotatable, symmetrical heating and cooling of the combustion chamber is attained and thermal expansion and contraction thereof will be symmetrical about its axis. Thus, thermal stresses in the combustion chamber are reduced to a minimum.

It will further be understood that, although the invention has been described with reference to the fans or pumps 14, 24 and 36, 38 being fixed to the rotating combustion chamber, it will be understood that this is not essential and therefore these fans or pumps can be separate from, but operatively associated with, the combustion chamber to achieve the same effect.

I claim:

1. Heat exchanger apparatus in which heat is transferred between two moving fluids, one of said fluids being the heating fluid and the other of said fluids being the fluid to be heated, which comprises a first flow path for said heating fluid, a second flow path for said fluid to be heated, a rotatable cylindrical combustion chamber the wall of which separates said first flow path of said second flow path, stationary heating means communicating with said first flow path, and fan or pump means operatively associated with said first and second flow paths to promote movement of said heating fluid relative to the interior surface of said rotatable chamber and to promote movement of said fluid to be heated relative to the exterior surface of said rotatable chamber, said rotatable chamber being in the form of a drum which is open at one end, said heating means being in the form of a gas burner arranged adjacent the closed end of said drum, a plurality of blade elements providing said fan or pump means being positioned on the open end ofsaid drum, and a plurality of blade elements being positioned on said closed end of said drum.

' 2. Heat exchanger apparatus in which heat is transferred between two moving fluids, one of said fluids being the heating fluid and the other of said fluidsbeing the fluid to be heated, which comprises a first flow path for said heating fluid, a second flow path for said fluid to be heated, a cylindrical outer casing, a rotatable combustion chamber arranged concentrically within and spaced from said outer casing, a stationary gas burner positioned within and at one end of said combustion chamber,'a stationary gas and combustion air feed pipe communicating with said gas burner and arranged concentrically with and spaced from said combustion chamber, the annular space between said outer casing and said combustion chamber providing said second flow path and the annular space between said combustion chamber and said feed pipe providing said first flow path, fan or pump means arranged in operative association with said one end of said combustion chamber to promote movement of said fluid to be heated along said second flow path relative to the exterior surface of said combustion chamber, and other fan or pump means operatively associated with the other end of said combustion chamber to promote movement of said heating fluid along said first flow path relative to the interior surface of said combustion chamber.

3. Apparatus as claimed in claim 2, in which a cooling or secondary air tube is positioned concentrically between said combustion chamber and said feed pipe.

4. Apparatus as claimed in claim 2, including a plurality of fixed radially disposed spaced blades positioned in said annular space providing said first flow path.

5. Apparatus as claimed in claim 4, in which said spaced blades are of a refractory material.

6. Apparatus as claimed in claim 2, including a plurality of fixed radially disposed spaced blades positioned in said annular space providing said first flow path, and elements of a refractory material arranged in the spaces between said blades. I

7. Heat exchanger apparatus in which heat is transferred between two moving fluids, one of said fluids being the heating fluid and the other of said fluids being the fluid to be heated, which comprises a first flow path for said heating fluid, a second flow path for said fluid to be heated, a cylindrical outer casing adapted, in use, to be mounted in an external wall of a building, a

rotatable combustion chamber arranged concentrically within and spaced from said outer casing, a stationary gas burner positioned within and at one end of said combustion chamber, a stationary gas and combustion air feed pipe communicating with said gas burner and arranged concentrically with and spaced from said combustion chamber, the annular space between said outer casing and said combustion chamber providing said second flow path which communicates with the interior of said building, and the annular space between said combustion chamber and said feed pipe providing said first flow path which communicates with atmosphere, fan or pump means arranged in operative association with said one end of said combustion chamber to promote movement of said fluid to be heated along said second flow path relative to the exterior surface of said combustion chamber, and other fan or pump means operatively associated with the other end of said combustion chamber to promote movement of said heating fluid along said first flow path relative to the interior surface of said combustion chamber.

8. Apparatus as claimed in claim 7, in which said annular space between said outer casing and said combustion chamber is divided longitudinally by an annular dividing wall which also encloses said fan or pump means, said dividing wall providing an inlet annulus which communicates with said interior of said building, and an air heating annulus through which air is drawn and expelled into said interior of said building by said fan or pump means.

9. Apparatus as claimed in claim 8, in which an annular end guide element is operatively associated with said inlet, annulus and said air heating annulus, which guide element is adjustable lengthwise of said combustion chamber whereby, in use, outside air can be drawn in by said fan or pump means.

10. Apparatus as claimed in claim 7, including a plurality of fixed radially disposed spaced blades positioned in said annular space providing said first flow path.

11. Apparatus as claimed in claim 10, in which said spaced blades are of a refractory material.

12. Apparatus as claimed in claim 7, including a plurality of fixed radially disposed spaced blades positioned in said annular space providing said first flow path, and elements of a refractory material arranged in the spaces between said blades. 

1. Heat exchanger apparatus in which hEat is transferred between two moving fluids, one of said fluids being the heating fluid and the other of said fluids being the fluid to be heated, which comprises a first flow path for said heating fluid, a second flow path for said fluid to be heated, a rotatable cylindrical combustion chamber the wall of which separates said first flow path of said second flow path, stationary heating means communicating with said first flow path, and fan or pump means operatively associated with said first and second flow paths to promote movement of said heating fluid relative to the interior surface of said rotatable chamber and to promote movement of said fluid to be heated relative to the exterior surface of said rotatable chamber, said rotatable chamber being in the form of a drum which is open at one end, said heating means being in the form of a gas burner arranged adjacent the closed end of said drum, a plurality of blade elements providing said fan or pump means being positioned on the open end of said drum, and a plurality of blade elements being positioned on said closed end of said drum.
 2. Heat exchanger apparatus in which heat is transferred between two moving fluids, one of said fluids being the heating fluid and the other of said fluids being the fluid to be heated, which comprises a first flow path for said heating fluid, a second flow path for said fluid to be heated, a cylindrical outer casing, a rotatable combustion chamber arranged concentrically within and spaced from said outer casing, a stationary gas burner positioned within and at one end of said combustion chamber, a stationary gas and combustion air feed pipe communicating with said gas burner and arranged concentrically with and spaced from said combustion chamber, the annular space between said outer casing and said combustion chamber providing said second flow path and the annular space between said combustion chamber and said feed pipe providing said first flow path, fan or pump means arranged in operative association with said one end of said combustion chamber to promote movement of said fluid to be heated along said second flow path relative to the exterior surface of said combustion chamber, and other fan or pump means operatively associated with the other end of said combustion chamber to promote movement of said heating fluid along said first flow path relative to the interior surface of said combustion chamber.
 3. Apparatus as claimed in claim 2, in which a cooling or secondary air tube is positioned concentrically between said combustion chamber and said feed pipe.
 4. Apparatus as claimed in claim 2, including a plurality of fixed radially disposed spaced blades positioned in said annular space providing said first flow path.
 5. Apparatus as claimed in claim 4, in which said spaced blades are of a refractory material.
 6. Apparatus as claimed in claim 2, including a plurality of fixed radially disposed spaced blades positioned in said annular space providing said first flow path, and elements of a refractory material arranged in the spaces between said blades.
 7. Heat exchanger apparatus in which heat is transferred between two moving fluids, one of said fluids being the heating fluid and the other of said fluids being the fluid to be heated, which comprises a first flow path for said heating fluid, a second flow path for said fluid to be heated, a cylindrical outer casing adapted, in use, to be mounted in an external wall of a building, a rotatable combustion chamber arranged concentrically within and spaced from said outer casing, a stationary gas burner positioned within and at one end of said combustion chamber, a stationary gas and combustion air feed pipe communicating with said gas burner and arranged concentrically with and spaced from said combustion chamber, the annular space between said outer casing and said combustion chamber providing said second flow path which communicates with the interior of said building, and the annular space between said combustion chamber and said feEd pipe providing said first flow path which communicates with atmosphere, fan or pump means arranged in operative association with said one end of said combustion chamber to promote movement of said fluid to be heated along said second flow path relative to the exterior surface of said combustion chamber, and other fan or pump means operatively associated with the other end of said combustion chamber to promote movement of said heating fluid along said first flow path relative to the interior surface of said combustion chamber.
 8. Apparatus as claimed in claim 7, in which said annular space between said outer casing and said combustion chamber is divided longitudinally by an annular dividing wall which also encloses said fan or pump means, said dividing wall providing an inlet annulus which communicates with said interior of said building, and an air heating annulus through which air is drawn and expelled into said interior of said building by said fan or pump means.
 9. Apparatus as claimed in claim 8, in which an annular end guide element is operatively associated with said inlet annulus and said air heating annulus, which guide element is adjustable lengthwise of said combustion chamber whereby, in use, outside air can be drawn in by said fan or pump means.
 10. Apparatus as claimed in claim 7, including a plurality of fixed radially disposed spaced blades positioned in said annular space providing said first flow path.
 11. Apparatus as claimed in claim 10, in which said spaced blades are of a refractory material.
 12. Apparatus as claimed in claim 7, including a plurality of fixed radially disposed spaced blades positioned in said annular space providing said first flow path, and elements of a refractory material arranged in the spaces between said blades. 